VoIP Voice and Fax Signal Processing

16.9 FAX UDPTL-BASED BIT RATE ON ETHERNET AND DSL INTERFACES

In Tables 16.7 and 16.8, T.38 fax bit rates are listed for basic fax rates and redundancies. In Table 16.7, bit rates are presented for no redundancy (R0) and 3-times redundancy (R3) on an Ethernet interface. The details on various headers [URL (National-Eth)] and their meaning are given in Chapter 11. For any other redundancy, the row marked “UDPTL, IFP, error recovery, redundancy” has to be changed with the corresponding values given in Table 16.6 for different redundancies.

On a DSL interface, the bit rate increases because of the additional header of PPPoE [Mamakos et al. (1999)], AAL5 trailer header, ATM cell splitting, and zero padding as shown in Table 16.8. More details on the headers are given in Chapter 11 for calculating the voice bit rate. A summary on T.38 bit rate requirements for Ethernet and DSL interfaces are given below:

• The minimum bit rate requirement from Ethernet is 17.6 kbps for the 2400 rate.
• The minimum bit rate from the DSL interface is 21.2 kbps for the 2400 rate.

  Table 16.7. VoIP Fax Packet Bit Rate on an Ethernet Interface

  

  Table 16.8. VoIP Fax Packet Bit Rate on DSL with PPPoE

  

• RFC2198 considers redundancy for the fax pass-through mode. For redundancy one, the RFC2198-based G.711 scheme takes ...